Note: 1.Adjust volume to the minimum before wearing. 2.Choose an earplug of slightly bigger size to avoid whistler. 3.Increase volume gradually to avoid sudden increase in sound. 4.If you hear a howling, check the ear (silica gel) is appropriate and whether the size of plug is tight, the appropriate choice of earplugs and plugged, make sure no air leakage. 5.Keep the ear plug clean.